1. Field of the Invention
The present invention relates to enhancing fluid flow from subterranean formations. More particularly, this invention relates to providing improved proppant matrixes within fractures in a subterranean formation.
2. Description of the Prior Art
Hydraulic fracturing is a technique for stimulating the production of a subterranean formation. The technique normally involves (1) injecting a viscous liquid through a wellbore into a formation at a chosen rate and pressure to overcome the earth's stresses and form a fracture in the formation; and (2) placing proppant particulates in the fracture to, inter alia, maintain the fracture in a propped condition when the injection pressure is released. The resultant propped fracture provides a conductive channel in the formation for fluids to flow to the wellbore.
The degree of stimulation afforded by the hydraulic fracture treatment is largely dependent on the permeability and width of the propped fracture. Thus, the productivity of the well in effect becomes a function of fracture conductivity. To enhance well productivity, it may be necessary to enhance fracture conductivity.
Oftentimes, to effectively prop open the fractures as well as prevent proppant particulate flowback, the proppant particulates are caused to consolidate into proppant matrixes within the fractures. One conventional means of doing this is to use resin-coated proppant particulates so that when the resin cures downhole, the proppant particulates can consolidate into a mass within the fractures. Other methods have also been used to facilitate the consolidation of the proppant particulates within the fractures.
Although consolidating the proppant particulates within a fracture may have some benefits, for example preventing proppant particulate flowback, such methods may adversely affect the conductivity of the fracture. That is, some methods of consolidating proppant particulates themselves may introduce a barrier to the free flow of fluids from the subterranean formation to the wellbore for subsequent production. Fracture conductivity may suffer as a result. This is undesirable as this may affect overall well productivity.
To counteract this potential problem, many different techniques have been developed. One technique involves adding calcium carbonate or salt to the proppant composition. When the proppant particulates consolidate, after a subsequent fluid is added to the wellbore, the calcium carbonate or salt is dissolved out of the matrix. At least one problem associated with this method is the incomplete removal of the calcium carbonate or salt if not adequately contacted with the subsequent fluid. Another method has been to add wax beads to the proppant composition. Once incorporated into the consolidated prop pant particulates, the wax beads melt as a result of the temperature of the formation. A problem with this method is that the wax may re-solidify in the well causing countless problems. Another method that has been used is to add an oil-soluble resin to the proppant composition, however, this method has not been successful because of, inter alia, nonuniform removal of the particles.
Another way to address fracture conductivity and proppant matrix permeability has been to use bigger proppant particulates. However, there are practical limits to the size of the proppant that may be used. For instance, if too large of particles are used, premature screen out at the perforations and/or fractures during the proppant stage of fracturing treatment often occurs as large size proppant particulates are being injected into the fractures. In addition, by using too large of proppant particles, the ability to control formation sand is lost as the formation sand or fines tend to invade or penetrate the large pore space of the proppant pack during production of hydrocarbons, thus choking the flow paths of the fluids.